Seventeen million people in Britain now use Vinted, a site built mostly for swapping unwanted jeans and trainers. On Sunday the culture secretary suggested it may soon sit alongside Instagram and TikTok on the list of services barred to children. Asked on the BBC's Sunday with Laura Kuenssberg programme whether ministers intended to keep under-16s off Vinted and eBay, Lisa Nandy said the government was "looking seriously at doing so". She gave no timetable and no detail.

The remark followed a Sunday Times report that the planned under-16 social media ban would be stretched to take in second-hand marketplaces. The paper said the worry was messaging tools that let strangers contact, and potentially groom, children. It also suggested Depop and Facebook Marketplace could be swept in. Nothing official confirms that part.

A ban that keeps widening

The government announced in June that under-16s would be shut out of ten of the biggest platforms, with the rules due to take effect in March next year. YouTube is on the list, though YouTube Kids, the version designed for young viewers, is not. A full roster hasn't been published. Ministers have said only that the test is whether a service exists to enable social interaction and lets users post material.

That definition is elastic, and the Vinted and eBay question shows how far it can stretch. Nobody would call a clothes-resale app a social network in the way Snapchat is one. But it has profiles, listings, reviews and, crucially, direct messages between adults and whoever happens to be on the other end of a sale. By the government's own logic, what counts is whether strangers can reach children, whatever the product calls itself.

The same reasoning already reaches into gaming. Platforms with livestreaming or stranger-contact features face restrictions, yet Roblox, the most popular game in Britain among eight to 12-year-olds, is not to be banned outright. Its chat function will be curtailed instead. So the model has two settings: exclusion for some services, feature-stripping for others. Which one a marketplace would get is unknown.

What the companies say

eBay's position is the simpler one. It already requires members to be over 18, because a listing amounts to entering a contract. A spokesperson said the company wanted to understand more and work constructively with ministers, adding that the details of any legislation were not yet clear. In practical terms, an eBay ban would formalise something the site claims to do already.

Vinted is messier. It is aimed at adults, but its terms let a parent or guardian open an account for a child, to be used under supervision. That provision is a plausible route for teenagers who want to sell last season's wardrobe, and a blanket ban would end it. In response, the company signalled that it was ready to talk to both ministers and the regulator. A spokesperson acknowledged that private messaging sits at the heart of how buyers and sellers do business on the site, but maintained that explicit or harmful material is not tolerated, that moderators and automated tools look for it, and that offenders can be expelled for good or referred to the police.

Those assurances may not settle the matter. Moderation is reactive by nature: it catches what it can find. A policy aimed at grooming risk starts from the assumption that some contact will always slip through, and that the safest design is to keep the audience out in the first place.

The enforcement problem nobody has solved

Which names go on the list is the easier part. Proving who is under 16 is harder. Australia brought in its own ban last year, and by most accounts many children there have found ways round it. British ministers have said they want a tougher approach. Last month Ofcom published its recommendations on the most effective ways to establish which users are over 16, and attention has moved from principle to mechanics.

This is where an extension to marketplaces gets awkward. Social networks hold years of behavioural data on their users and can, at least in theory, estimate age from it. A resale site holds far less. Age checks on tens of millions of accounts, many of them occasional sellers who log in twice a year, would be a heavy burden to bolt onto a service that has so far asked little of its users. Would a retiree clearing a loft on eBay really upload a face scan or an ID? Plenty may decide not to bother, and that's a commercial cost as much as a safety measure.

The NSPCC's head of online child safety, Rani Govender, argued that the priority is ensuring age verification functions in practice. In her view it addresses only one part of the problem. She wants firms obliged to embed protections for children in each platform, device and AI product, so that young people end up only on services suited to their age. A ban, however broad, is a gate and not a design standard.

Scope creep and its critics

Industry has begun pushing back on breadth. Matthew Sinclair, an official at the Computer and Communications Industry Association, a trade body for technology firms, warned ministers against letting the policy's reach grow beyond its original aim. Curbing under-16s' messaging, he said, would not stay confined to social media and would reach into services families rely on to keep in touch. He urged the government to keep any new restrictions proportionate and effective.

He has a point, though it comes from an interested party. Messaging is built into everything now: banking apps, school platforms, ride-hailing, games. Once the test becomes whether strangers can contact a child, the list of qualifying services is long, and legislators will have to decide where to stop. Drawing that line in primary law, rather than leaving it to a regulator's discretion, would give businesses certainty. It would also make later additions harder to wave through quietly.

What to watch

Three things will settle this. The first is the published list of covered platforms, which has been promised but not delivered, and which will show whether Nandy's "looking seriously" turns into a named entry for Vinted and eBay. The second is whether marketplaces get outright exclusion or the Roblox treatment, with messaging switched off for minors. The third is the cost of age verification at scale, which will fall on companies that, until now, never needed to ask.

March is not far away. If ministers add marketplaces, they will be telling millions of parents that a teenager selling a coat online belongs in the same regulatory category as one scrolling a feed at midnight. Some will accept that. Others will ask why the answer to grooming risk is a ban on a resale app, and not on the unsupervised contact itself.